The batse5bp package provides persistant local access to BATSE GRB data hosted at the CGRO SSC. It accesses both the BATSE GRB catalog (a collection of basic properties of all detected bursts, such as directions, intensities, and durations), and detailed GRB data (e.g., time series and spectral data).
The last official BATSE GRB catalog was the 4B catalog. The “current” catalog hosted at the SSC includes many GRBs observed subsequent to the 4B catalog. A 5B catalog, including data spanning to the end of the CGRO mission, was planned but was never completed (in particular, the sky exposure and efficiency tables were never computed). The “5bp” part of the package name denotes “5B, preliminary” (5Bp).
The full 5Bp GRB catalog is fetched, parsed, and stored locally when the user first loads the catalog. Subsequent loads access the stored copy. Detailed GRB data, which would be voluminous if downloaded en masse, is fetched transparently only when the user first attempts to access it. Only the requested data element, for a particular GRB, is fetched; it is cached locally for subsequent access.
Cached data is stored in a local file hierarchy with a structure resembling that of the SSC archive. Files and folders may be deleted within the local filesystem when no longer needed; they will be re-fetched as necessary. There is no monolithic database file, and no dependencies on 3rd-party database software.
batse5bp is currently a pure-Python package with only numpy and pyfits as dependencies (some example code here also relies on matplotlib). It is provided as a gzipped tar file containing the source code, “batse5bp-0.1.tar.gz”. It could be installed by unpacking and using the standard python setup.py install command. But the package is evolving so the recommended method is to use pip, which will allow easy uninstallation and replacement:
pip install batse5bp-0.1.tar.gz
To uninstall it:
pip uninstall batse5bp
To establish access to the 5Bp data, use the load_catalog() function:
from batse5bp import load_catalog # Load the catalog using the default database location (in the CWD): grbcat = load_catalog()
The first time it’s run, load_catalog() creates a database directory for storing fetched data, grabs the 5Bp catalog files from the SSC, parses them, collects the data in an object, and saves a serialized version of the object in the database for future access. The return value is the object providing access to the data, described below.
By default, the database directory is named “BATSE_5Bp_Data” and is created or accessed in the current working directory (CWD). To create it elsewhere, or with a different name, or to access a previously loaded database stored elsewhere, provide the database directory path as an argument to load_catalog().
load_catalog() returns a GRBCollection object that stores the data in GRB objects, one for each GRB.
A GRBCollection is a mapping (like a Python dict), providing access to the data for individual GRBs by using the BATSE trigger number (an integer) as a key. For example, grbcat returns a GRB instance providing access to the data for BATSE trigger 105, the first GRB observed by BATSE.
A GRBCollection is an ordered mapping, so if you iterate over it, you will access the GRB instances in order of the BATSE trigger number. (A standard Python dict returns its keys and items in an arbitrary order.)
For convenience, besides the standard dict keyword access, you can access GRB data via attributes, in two ways:
So all three of the following GRB instances are the same:
grb = grbcat grb2 = grbcat.t105 grb3 = grbcat.b910421
You can access the data and metadata for a GRB via the attributes and methods of its GRB instance.
Suppose you load the catalog in an interactive IPython session, and grab the GRB instance for trigger 105, as follows:
In : from matplotlib.pylab import * In : ion() # for interactive plotting in examples below In : from batse5bp import load_catalog In : grbcat = load_catalog() Loaded summary data for 2702 GRBs comprising the 5Bp catalog. In : grb = grbcat.t105
The string representation of grb (what gets shown by a print statement) provides a handy summary of the data in the burst’s catalog entries:
In : print grb Trigger: 105 Name: 4B_910421 TJD: 8367.384766 (RA, Dec) (long, lat) (deg): (270.68 24.76) ( 21.19 50.75) Drxn err (deg): 0.53 Complete? True Ch 1-4 fluence (ergs): 8.7e-07 1.3e-06 2.0e-06 1.0e-06 Ch 1-4 S/N: 8.0e+01 9.2e+01 1.1e+01 5.8e+00 64ms F_pk (cts), S/N, t: 12.76 23.46 3.84 T50, T90: 1.79 5.18 A: Ulysses, PVO rate increase O: Background source (Cyg X-1) Q: Data gap during burst accumulation; HV turnoff at T+38 s
Each item can be accessed as an attribute of grb; for example:
In : grb.trigger Out: 105 In : grb.desig Out: '910421' In : (grb.F64ms, grb.F64ms_err) Out: (12.761, 0.544)
These attributes contain, respectively, the trigger number, the designator in YYMMDD format (but omitting a possible lower-case suffix), and the 64 ms time scale peak flux and its error. See the grb module API documentation (in the Module Index, linked below) for more information about the attributes holding the catalog data.
Of note is the inclusion of information from the BATSE “Comments” table in the GRB instance:
In : grb.comments Out: [('A', 'Ulysses, PVO rate increase'), ('O', 'Background source (Cyg X-1)'), ('Q', 'Data gap during burst accumulation; HV turnoff at T+38 s')]
There were unusual circumstances for a number of GRBs that can impact interpretation of the data; the comments describe most such cases. A burst may have multiple comments associate with it, each with a flag identifying the comment type. The comments attribute is a list of 2-tuples containing the flag and its associated comment.
To understand the comments and the other catalog attributes, the authoritative reference is the catalog description text available at the SSC. The package provides local copies of the text for the various tables comprising the catalog in the docn module. For example, to see an explanation of the comments:
In : from batse5bp import docn In : print docn.comments The COMMENTS Table contains comments relevant to BATSE gamma-ray burst data found in the GROSSC BATSE burst catalog. Each category of comment is sorted by a flag identification and ordered by BATSE trigger number. A gamma-ray burst may have more than one entry or may have no entry. Flag Definition Q comments on data quality A additional observations by other instruments O general comments L comments on the gamma-ray burst coordinates T comments on the gamma-ray burst duration
The docn module contains similar text strings for the three other tables comprising the catalog: basic (with the trigger number, data, direction, overwrite flag, etc.), flux (with peak fluxes and fluences), and durn (with durations).
The docn module also provides convenience functions that will open important web pages at the SSC in your default browser. For convenience, these are all inserted into the batse5bp namespace:
The problems archive has text files identified by trigger number that describe problems with the data for a few dozen bursts, beyond what is mentioned in the Comments table.
GRB instances provide access to some of the detailed data for each GRB stored at the SSC in FITS files and files of other formats.
When a user firsts requests access to a particular detailed data type, the corresponding FITS file is fetched from the SSC and stored in the raw_cache directory within the database directory. The file is parsed, and the parsed data is cached elsewhere in the database. Future access of the data will access the already-parsed cached version. The FITS file is not deleted after parsing, but the user can delete any of the contents of the raw_cache directory (e.g., to reclaim space); FITS files will not be re-downloaded if they have been previously downloaded and parsed.
Users who examine FITS file contents not exposed by batse5bp may note that the sky locations in the FITS header for a trigger need not match the catalog location. The catalog locations were calculated after the locations in the detailed data FITS headers using improved algorithms. This is discussed further in the SSC trigger archive README file.
The simplest detailed data are light curve plots, stored as GIF image files at the SSC. Two plots are archived: one shows 64 ms count data from each of BATSE’s four discriminator (DISC) channels, the other shows the summed light curve. The show_lc() method fetches the images, creates a single image from them, and displays it using your default image viewer. The images are stored in the local database for future use. This is a good way to get a quick sense of what the data look like, but note that the archived light curves often show only a subset of the data.
The BATSE team has compiled three different DISC data types into a four- channel “64 ms” binned counts data set for each burst, stored as an ASCII file. These data are summed count rates (float-valued counts-per-second) from the subset of BATSE’s eight detectors that were triggered by a burst. Two of the data types contain genuine 64 ms data associated with a trigger: the PREB (PRE-Burst) and DISCSC (DISCriminator SCience) data. To extend coverage further, both before and after the time covered by PREB and DISCSC, the BATSE team used the continuously-recorded 256 ms DISCLA (DISCriminator Large Area) data to estimate 64 ms count rates prior to the PREB and after the DISCSC data. The early ASCII data thus has contiguous sets of 16 bins with identical count rates. Since the trigger need not be at the boundary of a 256 ms DISCLA interval, there is often a single set of fewer than 16 ASCII bins with identical rates, just before the PREB data.
A detailed description of the ASCII 64 ms data, copied from the SSC, is available as a string in the ascii64 module: ascii64.docn.
Note that the BATSE DISC pulse height channels are conventionally numbered from 1 to 4, but are accessed in Python code using 0-based indexing, i.e., numbered from 0 to 3.
GRB instances have an ascii64 attribute that provides access to the ASCII 64 ms data via an ASCII64 object with several attributes and one method providing different views of the data. The aim of this object is to report integer-valued counts (not rates), in the actual 64 and 256 ms bins used for measurements, by re-binning the subdivided DISCLA data, and converting the rate estimates back to counts. Presently this is only correctly done for the early (pre-PREB) DISCLA data. Fortunately, most bursts are short enough that late-time (post-DISCSC) DISCLA data will typically be ignored. But for long bursts, the user should use this ASCII data with caution, finding a way to handle the late-time subdivided DISCLA data. For the early mission, the DISCSC data duration is ~4 m; later in the mission the flight software was reconfigured to provide ~10 m of DISCSC data. The late-time DISCLA bins appear after these intervals.
For the attribute descriptions below:
One set of attributes makes the data with different binning separately available. early and t_early provide the counts and time bin boundaries for the early 256 ms DISCLA data. Similarly, late and t_late provide counts and times for the 64 ms PREB and DISCSC data (but including any late-time subdivided DISCLA data). In cases where there is a single truncated DISCLA bin before the PREB data, the mid and t_mid attributes contain the single photon count value in the truncated bin (as a length-1 NumPy integer array), and its time boundaries (as a length-2 float array). If there is no truncated DISCLA bin, the value of mid is None.
This block of code prints the last few counts in the early array, the mid counts (if present, else None), and the first few counts in the late array:
asc = grb.ascii64 print 'Early:', asc.early[0,-3:] print 'Mid:', asc.mid print 'Late: ', asc.late[0,:3]
A second set of attributes concatenates the data into single count and time arrays. counts contains all of the counts in time sequence. times contains the boundaries of all of the time bins.
The rates method returns a 3-tuple of NumPy arrays built from the concatenated data:
(centers, widths, rates) = grb.ascii64.rates()
centers contains the center times of the bins, widths contains the durations of the bins, and rates is a 4-row array containing counting rate estimates found by dividing the counts by the bin width. This is intended for plotting light curves. The following block of code uses matplotlib to plot the light curves for each channel in a common figure:
asc = grb.ascii64 t, w, r = asc.rates() figure(figsize=(12, 7)) for ch in range(4): plot(t, r[ch,:], '-', lw=2, alpha=.6) axvline(c='k') # show the trigger time xlabel(r'$t$ (s from trigger)') ylabel(r'$Rate$ (counts/s)')
(This plots the light curve as a curve; a histogram would be a more accurate representation of the data.)
GRB instances have a discsc_drms attribute providing access to the DRMs for the DISC channels of triggered detectors, via a DRMs_DISCSC object. This object contains DRM objects that hold the DRM data for each triggered detector. It also provides access to a DRM that sums the response of the triggered detectors.
Users should note that the archived DRMs are fairly coarsely sampled. Also, the response for DISC channel 4 is relatively flat over the tabulated range and is simply truncated at the high-energy end of the range (about 20 MeV; in fact, the response is typically rising slowly with energy above a few MeV). Integrals of the product of an incident flux model and the channel response will be inaccurate if the incident flux does not fall with energy at least as quickly as 1/E**2 above ~1 MeV.
discsc_drms.n_det is the number of triggered detectors.
Two discsc_drms attributes describe the common format of the DRMs for the triggered detectors and the summed response:
A DRM is a matrix defined so drm[i,j] is the response of channel i for the j‘th value of incident photon energy.
discsc_drms.detectors is a list of DRM instances, one for each triggered detector.
DRM instances have the following attributes:
The summed response of the triggered detectors (the detector-summed response) is available via similar attributes of discsc_drms itself: ch_bins, E_bins, drm, crv, and start.
The following block of code plots the detector-summed response for each of the four DISC channels in a single figure. Note that E_vals is set equal to the incident energy bin centers.
drms = grb.discsc_drms d0 = drms.detectors d1 = drms.detectors if 1: E_vals = (drms.E_bins[:-1] + drms.E_bins[1:]) / 2. for i in range(drms.n_ch): semilogx(E_vals, drms.crv[i], '-', lw=2) xlabel(r'$E$ (keV)') ylabel(r'$R_i(E)$ (cm$^2$)')
DRMs_DISCSC provides methods for numerical integration of the product of an incident spectrum model and the response function for each channel; the result is the expected number of detected photons (“counts”) in the channel. This quadrature capability is provided only for the detector-summed response.
The quadrature is done using an interpolatory inner product quadrature rule that uses evaluations of the response function and the spectrum at different points, to account for different availability and scales of variation of these two factors. Currently, only one rule is available: For each incident energy interval in a channel response vector, the rule uses the two response values at the interval boundaries, and three spectrum values within the interval, located at the zeroes of a 2nd-degree Legendre polynomial over the interval. This corresponds to linear interpolation of the response function, and 5th-degree polynomial interpolation of the spectrum, over each DRM incident energy interval.
Note that the DRMs for all channels share common incident energy bins, so the quadrature rules for all channels share common incident energy nodes.
To set up the rules for every channel of the detector-summed response for a burst’s DISC data, call the set_sum_prodquad method of the burst’s DRMs_DISCSC object. This defines a product quadrature rule for each channel; it also compiles the nodes (incident energy values used in the rules) and makes them available as an array via the quad_nodes attribute, so quad_nodes[j] returns the j'th energy value (the nodes are the same for all channels). The chan_quad(i, spec) method calculates the quadrature for channel i for input spectrum spec. The spectrum can be provided as a function (of incident photon energy), or as a vector of values pre-calculated on the nodes (this will be faster if results are sought for more than one channel). If a spectrum function is used that requires arguments besides the photon energy, those arguments can be provided to chan_quad as additional arguments; e.g., for a spectrum with parameters p1 and p2, the signature would be: chan_quad(i, spec, p1, p2).
The following block of code pre-calculates spectrum values and calculates the expected number of counts for BATSE channels 1 and 2 (indices 0 and 1). It assumes a spectrum function spec(E) exists, and that it can accept array arguments.
drms = grb.discsc_drms drms.set_sum_prodquad() svals = spec(drms.quad_nodes) # channels have common E values exp_cts_0 = drms.chan_quad(0, svals) exp_cts_1 = drms.chan_quad(1, svals)